The present invention is related generally to the field of orthodontics, and more particularly to systems and methods for measurement of teeth movements.
One objective in orthodontics is to move a patient's teeth to positions where the teeth function optimally and aesthetically. Conventionally, appliances such as braces are applied to the teeth of the patient by an orthodontist. Each appliance exerts continual force on the teeth and gradually urges the teeth toward their ideal positions. Over a period of time, the orthodontist adjusts the appliances to move the teeth toward their final destination.
Generally, the orthodontist specifies in a prescription the final tooth arrangement. The prescription is based on the orthodontist's knowledge and experience in selecting the intended final position of each tooth. The process of attaching the braces to teeth is tedious and painful to the patient. Additionally, each visit reduces the “chair-time” available to the orthodontist that could be used for another patient. Hence, the process of treating teeth using braces can be expensive.
New methods, such as those described in U.S. Pat. No. 5,975,893, allow the treatment to be planned in advance and all individual appliances to be fabricated at the outset of treatment. The appliances may thus be provided to the patient as a single package or system. Unlike braces, the patient need not visit the treating professional every time an adjustment in the treatment is made. While the patients will usually want to visit their treating professionals periodically to assure that treatment is going according to the original plan, eliminating the need to visit the treating professional each time an adjustment is to be made allows the treatment to be carried out in many more, but smaller, successive steps while still reducing the time spent by the treating professional with the individual patient. Moreover, the ability to use polymeric shell appliances that are more comfortable, less visible, and removable by the patient, greatly improves patient compliance, comfort, and satisfaction.
In the above system, and in other computer-aided teeth treatment systems, as a first step, a digital data set representing an initial tooth arrangement is obtained, referred to hereinafter as the IDDS. The IDDS may be obtained in a variety of ways. For example, the patient's teeth may be scanned or imaged using well known technology, such as X-rays, three-dimensional x-rays, computer-aided tomographic images or data sets, magnetic resonance images, etc. Methods for digitizing such conventional images to produce data sets useful in the present invention are well known and described in the patent and medical literature. Usually, however, the present invention will rely on first obtaining a plaster cast of the patient's teeth by well known techniques, such as those described in Graber, Orthodontics: Principle and Practice, Second Edition, Saunders, Philadelphia, 1969, pp. 401–415. After the tooth casting is obtained, it can be digitally scanned using a conventional laser scanner or other range acquisition system to produce the IDDS. The data set produced by the range acquisition system may, of course, be converted to other formats to be compatible with the software which is used for manipulating images within the data set, as described in more detail below. General techniques for producing plaster casts of teeth and generating digital models using laser scanning techniques are described, for example, in U.S. Pat. No. 5,605,459. After scanning, computer models of teeth on an upper jaw and a lower jaw are generated.
One advantage of the digital model teeth is the possibility of accurate measurements. Traditionally, dentists depend on manual measurement to measure dental features and orthodontic properties. They use rulers on teeth impression or X-rays images. Such manual measurements have limitations because they are manual processes and two dimensional measurements. Thus, the measurement results are not very precise and the rotation is difficult to measure. With the digital model, precise measurement and movement analysis can be performed. Using three-dimensional rigid body analysis accurate and complete movement of a tooth or the entire jaw can be calculated.
One application of the measurement is analyzing an orthodontic treatment. After any orthodontic treatment is performed, the outcome of the treatment needs to be examined. With the conventional measurement methods, such as measuring impressions or superimposing X-rays, there are many sources of uncertainties in the conclusions. Using the digital models, one can get a precise and complete analysis of treatment. The complete analysis can be achieved by taking two digital models, one before treatment and one after treatment, superimposing them in a virtual space, and calculating the movement of each tooth.